Electrophotographic marking is a well-known and commonly used method of copying or printing documents. Electrophotographic marking is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges, creating an electrostatic latent image of the desired document on the photoreceptor's surface. Toner particles are then deposited onto that latent image, forming a toner image. That toner image is then transferred from the photoreceptor onto a substrate such as a sheet of paper. The transferred toner image is then fused to the a substrate, usually using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
The foregoing broadly describes a black and white electrophotographic-printing machine. Electrophotographic marking can also produce color images by repeating the above process once for each color of toner that is used to make the composite color image. For example, in one color process, referred to herein as the REaD 101 process (Recharge, Expose, and Develop, Image On Image), a charged photoreceptive surface is exposed to a light image which represents a first color, say black. The resulting electrostatic latent image is then developed with black toner particles to produce a black toner image. The photoreceptor is then recharged, exposed, and developed using a second color, say yellow. The recharge, expose and develop process is then repeated for a third color, say magenta, and fmally for a fourth color, say cyan. The various color images are placed in superimposed registration so that a desired composite color image results. That composite color image is then transferred and fused onto a substrate.
The REaD IOI process can be implemented in various ways. For example, in a single pass printer wherein the composite fmal image is produced in a single pass of the photoreceptor through the machine. Other implementations require multiple passes of the photoreceptor through the various stations. For example, in a four-cycle printer only one color toner image is produced during each pass of the photoreceptor through the machine and wherein the composite color image is transferred and fused during the fourth pass. Another multiple pass implementation is in a two-cycle printer, wherein two different color toner images are produced during each of two pass of the photoreceptor through the machine and wherein the composite color image is transferred and fused during the last pass. REaD IOI can also be implemented in a five-cycle printer, wherein only one color toner image is produced during each pass of the photoreceptor through the machine, but wherein the composite color image is transferred and fused during a fifth pass.
An advantage of the multipass REaD/IOI processes is that they can be implemented at lower cost than the single pass REaD/IOI process. A multipass REaD/IOI system requires only one or two charging and exposure stations. Furthermore, at least in some configurations, a multipass REaD/IOI system can make multiple uses of various stations (such as using a charging station for transfer). Another advantage of multipass REaD/IOI systems it that they can be implemented with a small footprint (thus taking up less space on a desk).
Since exposing through an existing layer, developing over a developed layer, and transferring, fusing and cleaning multiple layers are more difficult than performing those tasks in non-REaD/IOI printers, and since the uniformity and quality requirements for color printing are generally more stringent than for black only printing, careful control of all processing steps in multipass REaD/IOI systems is critical. For example, if cleaning is performed incorrectly, or if the cleaning system is defective, residual debris and toner will contaminate subsequent images. Compounding the problem in REaD/IOI systems is the difficulty of transferring multiple toner layers. Poor transfer results in excess toner on the photoreceptor that the cleaning system must dispose of.
However, since low cost and small size are major advantages of REaD/IOI systems, the required process controls must be performed economically and without taking up an excessive amount of space. Therefore, a method of setting-up and diagnosing cleaning system components would be advantageous. Even more advantageous would be a method of setting-up and diagnosing cleaning system components that could be performed at low cost and that would not take up additional space.